Abstract: Fiber length, fiber content, water content and dry density are the main influencing factors of the strength of fiber red clay. The orthogonal experimental design method is used to study the effect of multi-factor coupling on the shear strength indexes c and φ of the fiber red clay. The test results are analyzed by the range analysis and variance analysis, and the optimal preparation process of c and φ and the significance of each influencing factor are determined. Based on the multivariate nonlinear regression theory, a multivariate nonlinear regression model of multi-factor for c and φ of the fiber red clay is established by sing the SPSS software. The experimental and analytical results show that the main order of the influence of four factors on the values of c and φ of the fiber soil is: water content＞dry density＞fiber content＞fiber length, in which the water content has a significant effect on c, dry density and fiber content. Dry density and fiber content have a certain effect on c, φ is obviously affected by water content and other factors have no obvious influence on φ. The change of level of each factor affects c more than φ. The multivariate nonlinear regression model of c and φ shows that the correlation coefficients of c and φ models are higher and more significant, and the linear relationship between the predicted and actual values is obvious, and the reliability of the model is determined. The research results are of important guiding significance for further research on the engineering characteristics and curing mechanism of the fiber-modified red clay.